Errrr if its been welded it might not b possible as it would not sit in the race pipe properly, or if you cut it the clamp might not go around properly.....
What idiot dont that, god you do get some strange people!
I honestly dont think you will be able to sort it out withoutgettin a new back box, only thing i can think of is melting the metal and seperating it, but for the hassle it propbs wudnt b worth it!
Hpe ive mabe helped a little!!
PS - the race sections sounds amazing, even better if you have a 4-2-1
EDIT - DAMN YOU PRED LOL OK SO I WAS WRONG